Ultra-violet light curable compositions for abrasion resistant articles

ABSTRACT

Inherently highly abrasion-resistant cast articles are prepared by polymerizing a composition comprising (I) as a first component from 0 to 100 parts of urethane polyacrylic ester and (II) as a second component, correspondingly from 100 to 0 parts of a composition containing (A) 30 to 60% by weight of a polyacrylic ester having 4 to 10 acryloyloxy groups, (B) 20 to 70% by weight of a polymerization shrinkage modifier, and (C) 0 to 30% of a diluent monomer. A source of free-radicals may be added to the composition.

FIELD OF THE INVENTION

This invention relates to polymeric abrasion-resistant articles and toresin compositions of compounds having a plurality ofethylenically-unsaturated carbamic ester groups useful for preparingsuch articles. As used throughout this specification,"ethylenically-unsaturated carbamic ester groups" refers to polymer sidechain groups having a single urethane linkage and terminal olefinicfunctionality. Articles made from resin compositions of the inventionreadily release from molds without use of release agents and areinherently abrasion-resistant.

BACKGROUND ART

Plastic articles have found a variety of use. For example, plasticoptical articles (such as video discs and ophthalmic lenses) are widelyused in place of such articles made from ground glass because the formerare light in weight and inexpensive to produce. As disclosed in U.S.Pat. Nos. 3,380,460 and 3,931,373, the most widely used plasticophthalmic lens material is polymerized diethylene-glycol bis(allylcarbonate). This polymer is characterized by excellent clarity,resistance to discoloration, high strength, and high impact resistance.However, polymerization of diethyleneglycol bis(allyl carbonate) isgenerally accompanied by high shrinkage during cure (e.g., from 11 to14%) and extended curing time (e.g., from 5 to 16 hours or more). Thehigh shrinkage levels create difficulties in the production of plasticophthalmic lenses from this material, particularly in the production oflenses having large differences in thickness between the center andedges of the lens. The extended cure times tie up production facilitiesand lead to inefficient utilization of the dies in which the lenses aremolded. Also, the thermal cure cycle used to polymerize the monomerconsumes large amounts of energy and undesirably thermally stresses theglass dies. Furthermore, the abrasion resistance of ophthalmic lensesmade from this monomer is not satisfactory. Consequently, such lensesare typically coated to improve their abrasion resistance. Theapplication of such coatings introduces problems such as adhesionfailure, crazing, index of refraction differences, and flow lines. Thislast problem is particularly troublesome with multifocal lenses.

Some polymerizable compositions containing four or moreethylenically-unsaturated carbamic ester groups and a copolymerizablediluent monomer have been broadly included in prior disclosures. See,for example, U.S. Pat. Nos. 3,509,234; 3,700,643; 3,782,961; 3,907,865;3,928,299; 3,954,584; 3,954,714; 4,006,024; 4,072,770; 4,108,840;4,112,017; 4,131,602; 4,133,723; 4,188,455; 4,228,232; 4,246,391;4,287,323; and 4,330,657; and U.K. Published Patent Application No.2,050,396 A.

These disclosures are related to thin-film or coating compositions suchas paints, varnishes, printing plates and photoresists, which aregenerally less than two millimeters thick. They fail to describe which,if any, of those compositions would have a desired balance of usefulproperties such as low polymerization shrinkage, low viscosity, absenceof coloration, high hardness, resistance to stress cracking, and anabrasion resistance of greater than 140 kilopascals (kPa) (20 psi).Additionally, they fail to teach how to obtain resins providing thedesired balance of properties which are useful for providing castarticles such as plastic ophthalmic lenses and which eliminate the needfor coating the articles with an abrasion resistant coating. Moreover,many of the compositions shown in these references are derived fromdiisocyanates (e.g., toluene diisocyanate), and the resultingcompositions have two or more urethane linkages in each side chain.These compositions generally have too high a viscosity to be useful foroptical casting purposes.

Compositions which contain four or more ethylenically-unsaturatedcarbamic ester groups attached to a polyester, polyether, orpolyacrylate backbone and articles prepared therefrom have beendisclosed in EPO 0068632, published May 1, 1983. The resins disclosedtherein can be diluted with up to 50% by weight of one or more diluentmonomers having one or more ethylenically-unsaturated groups and can becured in castings having a thickness greater than about 2 millimeters toform articles having Barcol hardness of greater than about 15. However,these compositions do not have an abrasion resistance greater than about700 kPa (about 100 psi).

DISCLOSURE OF THE INVENTION

The present invention provides highly abrasion-resistant articles thatreadily release from casting molds without having to employ the use ofrelease agents. The articles exhibit a resistance to abrasion by 000steel wool of at least 140 kPa (20 psi), preferably, 700 kPa (about 100psi). That is, they do not show visible scratches when rubbed with 000steel wool under a pressure of at least 140 kPa. The articles of theinvention may be prepared by polymerizing a colorless compositioncomprising per 100 parts by weight:

I. as a first component, from 0 to 100 parts by weight of a colorlessurethane polyacrylic ester;

II. as a second component, correspondingly from 100 to 0 parts by weightof a composition containing;

(A) from 30 to 60% by weight of a polyacrylic ester;

(B) from 20 to 70% by weight of a polymerization shrinkage modifier; and

(C) from 0 to 30% by weight of a diluent monomer; and

III. as a third component, from 0 to 5% by weight of I and II of asource of free radicals.

By the term "colorless" it is meant that the urethane polyacrylic estercomponent has an absorbance for visible radiation (i.e., from about 400to 600 nm) of less than about 0.1.

The urethane polyacrylic ester useful herein as the first component(component I) has the formula ##STR1## wherein: R¹ has the valence "a"and is the residue remaining after the removal of --NCO groups from anorganic polyisocyanate;

R² has the valence b+1 and is a polyvalent aliphatic group having 4 to10 carbon atoms (preferably 5 carbon atoms and, optionally, onecaternary oxygen atom);

R³ is --H or --CH₃ ;

a is a number having a value of at least 2; and

b is an integer of 3 to 5.

The composition useful as the second component (component II) hereincontains:

(A) from 30 to 60% by weight of a polyacrylic ester of an alkane, acycloalkane, or an azacycloalkane polyol, the polyol having up to 24carbon atoms and the ester having 4 to 10 acryloyloxy groups andnitrogen, when present, being covalently bonded to the carbon of acarbonyl group;

(B) from 20 to 70% by weight of a polymerization shrinkage modifier; and

(C) from 0 to 30% by weight of one or more diluent monomers having oneto three acryloyloxy groups copolymerizable with the compounds of (A)and (B).

The polymerization shrinkage modifier (part B of the second component)is preferably selected from the group consisting of

(1) a polymerizable carbamic compound having at least two groups selectfrom groups having the formulae ##STR2## and at least two acrylic groupsper 168 to 2000 of molecular weight and a molecular weight of 168 to5000, and

(2) a polymerizable poly(acryloyloxyalkoxy) alkane, cycloalkane orazacycloalkane defined hereinafter.

The polymerizable carbamic compound (part B(1) of the second component)is preferably selected from the group consisting of

(i) a carbamic ester having the formula ##STR3## in which: R³ is --H or--CH₃ ;

R⁴ is a divalent aliphatic group selected from --R⁶ -- and ##STR4## inwhich --R⁶ -- is an alkylene group having 1 to 6 carbon atoms or a 5- or6-membered cycloalkylene group having 5 to 10 carbon atoms;

R⁵ is a polyvalent linear structure obtained by removal of the hydroxylgroups from a monomeric or polymeric aliphatic polyol;

c is an integer of from 2 to 15 (preferably 3 to 6);

(ii) an acryloyloxyalkylisocyanurate of the formula ##STR5## in which:R⁷ is polyvalent aliphatic group selected from R⁶ and ##STR6## in whichR⁶ is as defined for Formula II and R¹¹ has a valence of g+1 and is apolyvalent aliphatic group having 4 to 10 carbon atoms (preferably 5carbon atoms) and, optionally, one catenary oxygen atom;

g is an integer of 1 to 3, and

(iii) a polyacrylamido compound having the formula ##STR7## wherein: R³is as defined above,

R⁸ is a linear, branched, or cyclic alkadiyl or -triyl group having 2 to10 carbon atoms and, optionally, up to 4 caternary oxygen atoms; and dis the integer 2 or 3.

The polymerizable material useful as part B(2) of the second componentmay be represented by the formula ##STR8## In this formula R³ and R⁴ areas defined above;

R⁹ is alkylene group having from 2 to 4 carbon atoms;

e is a number having a value of 1 to 3;

f is an integer of from 3 to 6; and

R¹⁰ is a residue of an alkane, cycloalkane, or azacycloalkane polyolhaving up to 24 carbon atoms wherein the nitrogen of the azacycloalkaneis covalently bonded to the carbon of a carbonyl group.

The source of free radicals (the third component) comprises from 0 to 5%by weight of total parts of the first and second components of anenergy-activatable source of free radicals.

The articles of the invention generally have a thickness greater thanabout 2 millimeters, an index of refraction greater than about 1.45 andless than about 1.75, a birefringence of essentially zero, lighttransmission greater than about 85%, yellow coloration less than about 4Gardner b units, a Barcol hardness greater than about 15 (with Barcolhardness being measured herein using Indenter No. "GYZJ 934-1",commercially available from the Barber-Coleman Company), and a heatdistortion greater than 200° C.

The present invention also provides a method for preparing cast opticalarticles comprising the steps of:

(1) mixing components I, II and, optionally, III of the polymerizablecomposition to form an optical casting resin,

(2) degassing the resin,

(3) introducing the degassed resin into a suitable mold, and

(4) effecting polymerization of the resin.

DETAILED DESCRIPTION OF THE INVENTION

The urethane polyacrylic ester of Formula I (the first component), ispreferably prepared by reaction of one mole of di- or triisocyanate,respectively, with 2 to 2.2 moles or 3 to 3.3 moles of apolyacryloyloxyalkanol. The polyacryloyloxyalkanols can be considered aspolyols having 4 to 10 carbon atoms and 4 to 6 hydroxy groups, of whichall but about one hydroxyl group has been esterified with an acrylicacid. The term "acryloyloxy" as used herein includes both theacryloyloxy group and the methacryloyloxy group. Representative examplesof useful polyacryloyloxyalkanols are pentaerythritol triacrylate,dipentaerythritol pentaacrylate,2,2,3,3-tetra(acryloyloxymethyl)propanol, arabitol tetraacrylate, andsorbitol pentaacrylate and the corresponding methacrylates.

Isocyanates that can be used in the preparation of the urethanepolyacrylic ester include the aliphatic, cycloaliphatic, and aromaticpolyisocyanates having at least two isocyanate groups. Such compoundsare known and include 2,4-tolylene diisocyanate,3,5,5-trimethyl-1-isocyanato-3-isocyanatomethylcyclohexane (also calledisophorone diisocyanate), hexamethylene diisocyanate,1,3,5-tris(6-isocyanatohexyl-1,3,5-triazine-2,4,6(1H, 3H, 5H)trione,1,3-di(isocyanatoethyl)hydantoin, 2,2,4-trimethylhexamethylenediisocyanate and 1,3,5-benzenetriisocyanate. Other suitablepolyisocyanates are described in U.S. Pat. Nos. 3,641,199; 3,700,643;and 3,931,117, among many others.

The polyacrylic ester useful as part A of the second component hereincomprises one or more polyacrylic acid esters of an alkane, cycloalkaneor azacycloalkane polyol, the polyol having up to 24 carbon atoms.Nitrogen, when present, is covalently bonded to a carbonyl group.Examples of such compounds include pentaerythritol tetraacrylate,dipentaerythritol hexaacrylate, pentaacryloyloxymethylethane,3,3,7,7-tetra(acryloyloxymethyl)-5-oxanonane, arabitol pentaacrylate,sorbitol hexaacrylate and the corresponding methacrylates, and1,3-bis(2-acryloyloxyethyl-5,5-dimethyl)-2,4-imidazolidinedione.

Polymerization shrinkage modifiers useful as part B of the secondcomponent are materials whose mechanism of operation is not understoodbut which overcome the problems of shrinkage encountered in thepolymerization of highly acrylated monomers such as pentaerythritoltetraacrylate. Such monomers, without the modifier, polymerize rapidlyand shrink during polymerization to such an extent that polymersobtained therefrom are full of internal stress and are extremelybrittle. The shrinkage modifiers useful herein are believed to releasethis stress and allow the formation of highly acrylated polymers havingessentially no internal stress.

Suitable shrinkage modifiers are polymerizable compounds having aplurality of carbamic linkages (Part B(1)) or a plurality of etherlinkages (Part B(2)).

Carbamic esters (Part B(1)(i)) of the optical casting resin arepreferably prepared by reacting one or more monoisocyanate-substituted,addition-polymerizable ethylenically-unsaturated organic compounds (suchcompounds being sometimes referred to hereafter as"ethylenically-unsaturated isocyanates") with at least one polyol whichcan be any aliphatic monomeric or polymeric polyol. The polyolpreferably is a polyester polyol, polyether polyol or polyacrylatepolyol (such polyester polyols, polyether polyols, and polyacrylatepolyols being sometimes referred to collectively hereafter as"polyols"), said polyols having at least two hydroxyalkyl orhydroxycycloalkyl groups per molecule. The amount of reactants and timeof reaction are chosen so as to result in consumption of essentially allfree isocyanate groups in the reaction mixture as determined by, forexample, infrared analysis. Generally, about 0.8 to 1 mole ofethylenically-unsaturated isocyanates are used per mole of hydroxylgroups in the polyols. Preferably, the reaction betweenethylenically-unsaturated isocyanates and polyols is carried out in thepresence of a suitable catalyst such as dibutyltin dilaurate. Thereaction is generally performed in a suitable mixing vessel undersubstantially anhydrous conditions at temperatures from about 25° C. to100° C. for ten minutes or more, utilizing bath or continuousprocessing.

Preferred ethylenically-unsaturated isocyanates are compounds having thegeneral formula ##STR9## wherein R³ and R⁴ are as defined previously.Preferably, R³ is methyl and R⁴ is a divalent carbonyloxyalkyleneradical having 2 to 7 carbon atoms.

Preferred compounds of Formula VI are isocyanatoalkyl acrylates andmethacrylates such as isocyanatomethyl acrylate, 2-isocyanatoethylacrylate, 2-isocyanatoethyl methacrylate, 3-isocyanatopropyl acrylate,3-isocyanatopropyl methacrylate, and 6-isocyanatohexyl acrylate. Apreferred ethylenically unsaturated isocyanate is 2-isocyanatoethylmethacrylate. Other useful compounds of the Formula VI type includeethylenically-unsaturated isocyanate esters such as allyl isocyanate,methallyl isocyanate, 4-ethenylcyclohexyl isocyanate and2-(2-acryloyloxyethoxy)ethyl isocyanate. The ethylenically-unsaturatedisocyanates of Formula VI can be prepared using methods known to thoseskilled in the art of organic synthesis.

Monomeric aliphatic and polymeric polyols which can be used to preparethe polymerizable carbamic ester resins for making the optical articlesof this invention preferably contain only carbon, hydrogen and oxygen,but can, if desired, contain other chain atoms (e.g., sulfur atoms) orsubstituent groups (e.g., chloromethyl groups) which do not interferewith the functioning of the polymerizable carbamic ester as an opticalcasting resin. They have at least two hydroxyl groups, a hydroxylequivalent weight of 31 to 1000, preferably 59 to 300, and a molecularweight of 62 to 5000, preferably 118 to 2100.

The monomeric aliphatic polyols are those polyols that do not containrepeating units in contrast to the polymeric aliphatic polyols which cancontain from 2 to about 100 units, such as --CH₂ CH₂ O--, that areconnected together in a chain. Monomeric aliphatic polyols are wellknown and include, for example, alkane polyols such as ethylene glycol,1,3-propylene glycol, 1,4-butylene glycol, glycerine, neopentyl glycol,trimethylolpropane, tetramethylolethane, pentaerythritol,dipentaerythritol, erythritol, arabitol and sorbitol.

Polymeric polyols that can be used to prepare the polymerizable carbamicester resin polyols have, as the name implies, a backbone that containsrepeating units. The polyols include the polyester, polyether, andpolyacrylate polyols having at least two hydroxyl groups. The polymericpolyols preferably have a hydroxyl equivalent weight between 175 and300. If polyols having hydroxyl equivalent weight greater than about1000 are used, the resulting polymerizable carbamic ester resin willhave inadequate hardness for use as an optical casting resin. Polyesterpolyols are preferred polyols for use in preparing the polymerizablecarbamic ester resins of this invention.

Suitable polyester polyols can be prepared by esterifying: (a) C₂₋₁₅aliphatic acyclic or C₄₋₁₅ alicyclic polyols having three or morehydroxyl groups per molecule, with (b) polycarboxylic acid (preferablydicarboxylic acids) selected from C₄₋₁₂ aliphatic acyclic polycarboxylicacid, C₅₋₈ alicyclic polycarboxylic acids, C₅₋₁₅ aromatic polycarboxylicacids, or methyl or ethyl esters or anhydrides of such polycarboxylicacids. Such polycarboxylic acids, methyl or ethyl esters thereof, andanhydrides thereof are sometimes referred to collectively hereafter as"polycarboxylic acids". Optionally, C₂₋₁₅ aliphatic acyclic diols, C₄₋₁₅alicyclic diols, C₂₋₆ omega-hydroxyalkanecarboxylic acids or lactonescan be added to the above-described mixture of C₂₋₁₅ aliphatic acyclicor C₄₋₁₅ alicyclic polyols and polycarboxylic acids. The ratio of totalmoles of aliphatic acyclic polyols, alicyclic polyols, aliphatic acyclicdiols, and alicyclic diols to total moles of polycarboxylic acids,omega-hydroxyalkanecarboxylic acids, and lactones should be such as toprovide essentially complete esterification of carboxylic acid groups,and a product polyester having a molecular weight no more than about5000. Sufficient aliphatic acyclic or alicyclic polyols should be usedto provide a product polyester polyol having at least four hydroxylgroups per molecule.

Especially preferred polyester polyols are esters derived from aspecified amount of certain cyclic compounds, and are prepared byemploying about 0.02 to 0.5 moles of cyclic compounds selected from: (a)C₅₋₈ alicyclic dicarboxylic acids or anhydrides thereof, (b) C₅₋₁₅aromatic dicarboxylic acids or anhydrides thereof, or (c) C₄₋₁₅cycloalkylene diols per mole of C₂₋₁₅ aliphatic acyclic polyols. Theremainder of the compounds from which said polyester polyol is derivedcomprise acyclic compounds. The resulting polyester polyols can be usedto prepare polymerizable carbamic ester resins which provide castoptical articles having especially high heat deflection temperature(e.g., above about 200° C.) and Barcol hardness (e.g., greater than 20as measured using Indentity No. "GY-ZJ 934-1").

Suitable polyester polyols can also be prepared by combining, on a molarbasis, one mole of C₄₋₁₅ polyols having four or more hydroxyl groups permolecule and about 4 to 15 moles of C₂₋₆ omega-hydroxyalkanecarboxylicacids or lactones. The reactants should be combined in amountssufficient to esterify essentially all carboxylic acid groups presentand provide a product polyester polyol having a molecular weight no morethan about 5000, and having at least four hydroxyl groups per molecule.

Aliphatic acyclic polyols which can be used to prepare theabove-described polyester polyols include ethylene glycol,1,4-butanediol, 1,3-butanediol, 2,2-dimethyl-1,3-propanediol,1,6-hexanediol, 1,12-dodecanediol, glycerine,2,-hydroxymethyl-1,3-propanediol, 1,1,1-tri(hydroxymethyl)propane,1,2,4-butanetriol, 1,2,6-hexanetriol, dipropylene glycol,pentaerythritol, dipentaerythritol, tripentaerythritol, sorbitol,disorbitol, and mixtures thereof.

Alicyclic polyols which can be used to prepare the above-describedpolyester polyols include 1,4-cyclohexanediol,1,4-bis(hydroxymethyl)cyclohexane, bis(4-hydroxycyclohexyl)-methane,bis(4-hydroxymethylcyclohexyl)methane,2,2-bis(4-hydroxycyclohexyl)propane, and mixtures thereof.

Suitable polycarboxylic acids which can be used to prepare theabove-described polyester polyols include succinic acid, maleic acid,glutaric acid, 2,2-dimethylsuccinic acid, pimelic acid, adipic acid,sebacic acid, dilactic acid, tetrahydrophthalic acid, hexahydrophthalicacid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalicacid, tetrachlorophthalic acid, 2,2'-benzophenonedicarboxylic acid,4',4'-diphenylmethanedicarboxylic acid, 2,5-naphthalenedicarboxylicacid, dimethyl succinate, diethyl adipate, dimethyl tetrahydrophthalate,dimethyl phthalate and mixtures thereof.

The above-described polyester polyols can be formed using procedureswell knwon in the art. Usually, the polyester polyol is formed by directesterification, ester exchange, or condensation reaction between theC₂₋₁₅ aliphatic acyclic or C₄₋₁₅ alicyclic polyols, the polycarboxylicacids and, where used, the omega-hydroxyalkanecarboxylic acids, orlactones. Generally, the above reactants are combined, preferably in thepresence of a suitable esterification catalyst, and heated to atemperature sufficient to distill off volatile side products, preferablyunder an inert atmosphere such as carbon dioxide or nitrogen. Thereaction is completed by heating the reactants under vacuum for about 2to 24 hours or more, until the acid number of the reaction mixture fallsbelow about 5 milligrams of KOH per gram of reaction mixture and thehydroxyl equivalent weight of the reaction mixture is between about 31and 1000, preferably between about 59 and 300.

Suitable commercially available polyester polyols include "Lexorez"5171-280, 5171-260 and 5171-200 (polyester polyols derived fromtrimethylolpropane, dipropylene glycol, adipic acid, and phthalicanhydride, having a hydroxyl functionality of 5 to 7, and hydroxylequivalent weights of 200, 216 and 280, respectively), "Lexorez" XP142-144 (polyester polyol derived from neopentyl glycol,trimethylolpropane, and adipic acid, having a hydroxyl functionality of5 to 7, a hydroxyl equivalent weight of 200, and a molecular weight of1000), and "Rucoflex" F-2016-185 (polyester polyol having a nominalhydroxyl functionality of 4, a nominal hydroxyl equivalent weight of300, and a nominal molecular weight of 1200). The "Lexorez" resins arecommercially available from Inolex Corporation while "Rucoflex"commercially available from Hooker Chemical Company.

Polyether polyols which can be used to prepare the polymerizablecarbamic ester resins of this invention are preferably prepared by thecondensation of aliphatic polyols having at least two hydroxyl groupsper molecule with alkylene oxides, in the presence of an alkalinecatalyst. Preferred aliphatic polyols for use in the preparation of suchpolyether polyols include erythritol, pentaerythritol, mannitol,sorbitol, and mixtures thereof. Preferred alkylene oxides for use in thepreparation of such polyether polyols include butylene oxide, propyleneoxide, and mixtures thereof.

Useful commercially available polyether polyols include "Niax" LS-490(polyetherpolyol having a hydroxyl functionality of 6, a hydroxylequivalent weight of 114, and a molecular weight of 684) from UnionCarbide Co.

Polyacrylate polyols which can be used to prepare the polymerizablecarbamic ester resins of this invention are polymers of hydroxyalkylacrylates or methacrylates prepared with or without othercopolymerizable ethylenically-unsaturated monomers that have beenpolymerized in the presence of a sufficient amount of chain terminatorto limit the molecular weight of the resulting polyacrylate polyol tobelow about 5000.

Suitable polyacrylate polyols include "TSAX" 11071, (polyacrylate polyolhaving a hydroxyl equivalent weight of 900), available from HenkelCorporation.

Acryloyloxyalkylisocyanurate compounds of Formula III are isocyanuratesthat have been substituted by acryloyloxy groups. Such compounds andtheir preparation are disclosed in U.S. Pat. No. 3,808,226 (Habermeieret al), which is incorporated by reference. Examples of these compoundsare1,3,5-tris(6-[2,2,2-(triacryloyloxymethyl)ethoxycarbonylamino]hexyl)-s-triazine-(1H,3H,5H)trione,1,3,5-tris(4-[2-(methacryloxy)ethoxy-carbonylamino]-cyclohexyl)-s-triazine-2,4,6(1H,3H,5H)trioneand1,3,5-tris(3-[2,2,2-(triacryloyloxymethyl)ethoxy]-2-hydroxypropyl)s-triazine-2,4,6(1H,3H,5H)trione.

Polyacrylamido compounds of Formula IV are well known and are thereaction product of polyamino compounds with acrylic or methacrylicacid, their halides, anhydrides or esters of a C₁ to C₄ alkanol.Examples of polyacrylamido compounds include 1,2-diacryloylaminoethane,1,3-diacryloylaminopropane, 1,4-diacryloylaminobutane,1,6-diacryloylaminohexane, 1,4-bis(acryloylaminomethyl)cyclohexane,1,10-diacryloylaminodecane, 3,3-bis(acryloylaminomethyl)propane,1,2,3-triacryloylaminopropane, 1,3,5-triacryloylaminocyclohexane, and1,5-diacryloylamino-3-oxapentane and the corresponding methacrylaminocompounds.

Polymerizable poly(acryloyloxyalkoxy) compounds of Formula V (PartII-2-b) of the polymerizable composition are the polyacrylic esters ofpolyols that are obtained by reaction of an alkane, cycloalkane, orazacycloalkane polyol with an alkylene oxide. Examples of suchpolymerizable esters include1,1,1-tris(2-acryloyloxyethoxymethoxy)propane,tetra(2-acryloyloxypropoxymethoxy)methane, the hexaacrylate ester ofhexapropoxylated dipentaerythritol, the pentaacrylate ester ofpentabutoxylated arabitol, and the triacrylate ester of triethoxylated1,3,5-trihydroxyethyl isocyanurate.

Diluent monomers for use in the above-mentioned compositions arefree-radical polymerizable monomers such as olefins which preferablycontain at least one acrylyl or methacrylyl radical. Examples ofsuitable diluent monomers include acrylic acid, methacrylic acid,acrylamide, methacrylamide, methyl acrylate, methylalpha-chloroacrylate, ethyl acrylate, hexyl acrylate, 2-ethylhexylacrylate, butoxyethoxyethyl acrylate, neopentylglycol diacrylate,pentaerythritol mono-, di-, or triacrylate or mixtures thereof, isodecylacrylate, trimethylolpropane mono-, di-, or triacrylate or mixturesthereof, 2-phenoxyethyl acrylate, glycidyl acrylate, 2-ethoxyethylacrylate, 2-methoxyethyl acrylate, tetrahydrofurfuryl acrylate,2,2,2-trifluoroethyl acrylate, cyanatoethyl acrylate,2-carbamoyloxyethyl acrylate, 2-(N-methylcarbamoyloxy)ethyl acrylate,2-(N-butylcarbamoyloxy)ethyl acrylate, methacrylates of the aboveacrylates, and mixtures of the above diluent monomers. Other diluentmonomers which can be used include acrylonitrile, styrene,4-methyl-styrene, alpha- methylstyrene, alpha-chlorostyrene,4-bromostyrene, cyclopentadiene, vinyl chloride, vinylidene chloride,vinyl acetate, vinyl methyl ketone, isopropyl vinyl ketone, and mixturesthereof. Preferably, the diluent monomers are added to the polymerizablecarbamic compound after formation thereof, rather than being presentduring formation of the polymerizable carbamic compound, in order toavoid possible yellowing of the polymerizable carbamic ester resin.

By selecting various diluent monomers or mixtures thereof, the index ofrefraction and cure time of the cast articles of this invention can beadjusted within limits. For example, mixtures of neopentylglycoldiacrylate and 2-phenoxyethyl acrylate can be used as diluent monomers,and the ratio of these two diluent monomers can be altered to vary theindex of refraction of the resulting cast articles between about 1.50 to1.54. This is particularly useful when it is desired to prepare castoptical articles. Other diluent monomers can be similarly used. Curetimes for casting resins containing various diluent monomers aredescribed in more detail in the examples below.

The index of refraction of the cast articles of this invention can bevaried by other means if desired. For example, increasing the aromaticcontent of the casting resin will tend to increase the index ofrefraction of articles cast therefrom. Also, use of halogenateddicarboxylic acids, halogenated polyols, or halogenated diluent monomersto form the casting resins will tend to increase the index of refractionof articles cast therefrom, at some decrease in resistance of the curedarticle toward yellowing after exposure to sunlight (i.e., weatheringresistance).

The casting resins of this invention optionally contain zero to aboutfive percent by weight of an energy-activatable source of free radicals,i.e., a free-radical polymerization initiator which generates orliberates free radicals upon addition to the casting resins of energysuch as thermal energy, actinic radiation, or electron beam radiation.Curing techniques such as thermal energy and actinic radiationordinarily require the use of positive amounts (i.e., more than zeropercent by weight) of polymerization initiator. No polymerizationinitiator (i.e., zero percent by weight) is ordinarily required whencuring techniques such as electron beam energy are used. Usefulfree-radical polymerization initiators are further described, forexample, in Chapter II of "Photochemistry" by Calvert and Pitts, JohnWiley & Sons (1966).

Thermally-activated free-radical polymerization initiators includeorganic peroxides, organic hydroperoxides, and other known initiators,such as benzoyl peroxide, tertiary-butyl perbenzoate, cumenehydroperoxide, isopropyl peroxydicarbonate, azobis(isobutyronitrile),and the like. The preferred free-radical polymerization initiators foruse in this invention are photopolymerization initiators which releasefree-radicals when the optical casting resins of this invention areirradiated with suitable electromagnetic radiation.

Useful photopolymerization initiators include acyloin and derivativesthereof such as methyl benzoyl formate, benzoin, benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether,and alpha-methylbenzoin, diketones such as benzil and diacetyl, organicsulfides such as diphenyl monosulfide, diphenyl disulfide, decyl phenylsulfide, and tetramethylthiuram monosulfide, S-acyl dithiocarbamatessuch as S-benzoyl-N,N-dimethyldithiocarbamate, phenones such asacetophenone, alpha,alpha,alpha-tribromoacetophenone, alpha,alpha-diethoxyacetophenone, ortho-nitro-alpha,alpha,alpha-tribromoacetophenone, benzophenone, and4,4'-bis(dimethylamino)benzophenone, and sulfonyl halides such asp-toluenesulfonyl chloride, 1-naphthalenesulfonyl chloride,2-naphthalenesulfonyl chloride, 1,3-benzenedisulfonyl chloride,2,4-dinitrobenzenesulfonyl bromide and p-acetamidobenzenesulfonylchloride. Methyl benzoyl formate is a preferred photopolymerizationinitiator, as it provides cast optical products having low yellow color.

For curing techniques such as thermal energy and actinic radiation, thefree-radical polymerization initiator is ordinarily used in amountsranging from about 0.01 to 5 percent by weight compared to the totalweight of optical casting resin. When the polymerization initiatorquantity is less than about 0.01 percent by weight, the polymerizationrate of the casting resin is slowed. When the polymerization initiatoris used in amounts greater than about five percent by weight, noappreciable increase in polymerization rate is observed compared tocompositions containing about five percent by weight of polymerizationinitiator. Preferably, about 0.05 to 1.0 percent by weight ofpolymerization initiator is used in the polymerizable casting resins ofthis invention cured by thermal energy or actinic radiation.

Adjuvants which are conventionally used in resins for cast articles,particularly optical articles, such as inhibitors, antioxidants, dyes,mold release agents, and the like can be added if desired. However, amold release agent is generally not required with the casting resins ofthis invention, and the absence of a mold release agent represents amanufacturing advantage of this invention.

Several physical properties of the casting resins of this invention canbe adjusted by, for example, varying the amounts and types of monomersused to synthesize the polymerizable carbamic ester resin, varying therelative amounts of polymerizable carbamic ester resin(s) and diluentmonomer(s); varying the types of diluent monomers, or using a mixture ofdiluent monomers. For example, the hardness of the cured casting resincan be increased by: (1) increasing the vinyl functionality ordecreasing the molecular weight of the polymerizable carbamic compound,(2) using a polymerizable carbamic ester derived from a polyester polyolprepared from a mixture of cyclic compounds and aliphatic acyclicpolyol, containing the above-described ratio of about 0.02 to 0.5 molesof cyclic compounds selected from alicyclic dicarboxylic acids, aromaticdicarboxylic acids, anhydrides thereof, or cycloalkylene diols per moleof aliphatic acyclic polyol, or (3) by increasing the olefinicfunctionality of the diluent monomer. Shrinkage of the casting resinduring cure can be reduced by increasing the molecular weight of thepolymerizable carbamic ester resin. Ordinarily, it is desirable tominimize yellow coloration in certain plastic articles such as opticalarticles both at the time of manufacture and after exposure to sunlight.Tendency toward initial yellow coloration can be reduced by employingpurified ingredients and by utilizing the preferred photoinitiatormethyl benzoyl formate. Weathering resistance can be increased byminimizing aromatic content in the backbone of Formula I, above, or byadding to the casting resin one or more ultraviolet light absorbers suchas hydroxybenzophenones (e.g., 2,4-dihydroxybenzophenone and2-hydroxy-4-methoxybenzophenone), carboxybenzophenones (e.g.,2-hydroxy-4-carboxybenzophenone), benzotriazoles (e.g.,2-(2'-hydroxy-5'-methylphenyl)benzotriazole), cyanoacrylates (e.g.,2-ethylhexyl-2-cyano-3,3-diphenylacrylate), and the like. Abrasionresistance of the cured cast article can be increased by using a diluentmonomer having a high level of olefinic functionality (e.g.,pentaerythritol tetraacrylate or trimethylolpropane triacrylate). Theworking environment in production operations can be improved by using adiluent monomer such as neopentylglycol dimethacrylate orn-butylcarbamoyloxyethyl acrylate. Viscosity of the casting resin can bereduced by utilizing a diluent monomer having low viscosity and/or highsolvating power with respect to the polymerizable carbamic ester resin.

The articles of this invention include articles which are currentlyprepared from ground glass or cast plastic, such as ophthalmic lenses,diffraction gratings, Fresnel lenses, and video discs. Such articlesgenerally have a thickness of about 2 mm or more, and can be preparedfrom casting resins of this invention which are made by mixing in asuitable vessel, in any convenient order, the diluent monomer andpolymerizable carbamic ester resin, to provide 100 parts of acomposition having a viscosity less than about 1000 poise at 20° C. Tothe resulting mixture is then added up to about five parts by weight ofpolymerization initiator, if desired. Mixing is continued until thecomponents of the composition are in a single phase. If prepared usingphotoinitiator, the composition is preferably stored in the dark orunder a suitable safelight until ready for use.

At the time of use, the composition is preferably degassed using avacuum of less than about 25 Torr or by flowing the composition in athin film past a suitable boundary. The degassed composition isintroduced, preferably using a pressure of about 2 to 10 Kg/cm², into amold corresponding to the shape of the article which is desired to beprepared. Such molds are generally made of glass or glass and metal andmay include a resilient gasket which compensates for polymerizationshrinkage. Casting resins of this invention containingthermally-activated polymerization initiators are cured or polymerizedto a hard, transparent state by placing the filled mold into a forcedair oven or water bath at a temperature of about 50° C. to 100° C. for aperiod of about 1 to 12 hours, followed by an increase in temperature toabout 75° C. to 150° C. over a period of about 1 to 12 hours, followedby removal of the molds from the oven or bath, opening of the molds, andcooling of the cured articles contained therein.

For casting resins of this invention containing photopolymerizationinitiator, the molds are filled as described above, placed under asource of electromagnetic (e.g., actinic) radiation such as a highenergy ultraviolet source having an output of, e.g., about 25 to 250watts/cm of source length. Preferably, the duration and intensity ofsuch exposure is adjusted to provide for partial (e.g., about 50 to 80percent) polymerization of the resin contained in the molds. Thepartially polymerized articles can then be removed from the molds. Cureor photopolymerization of the articles to a hard, transparent state canbe completed by exposure of the articles (unsupported by molds) tosufficient additional radiation to complete the polymerization of sucharticles. If desired, final cure can be carried out using thermalenergy.

Preferred photoinitiation energy sources emit actinic radiation, i.e.,radiation having a wavelength of 700 nanometers or less which is capableof producing, either directly or indirectly, free radicals capable ofinitiating addition polymerization of the optical casting resins of thisinvention. Particularly preferred photoinitiation energy sources emitultraviolet radiation, i.e., radiation having a wavelength between about180 and 460 nanometers, including photoinitiation energy sources such asmercury arc lights, carbon arc lights, low, medium, or high pressuremercury vapor lamps, swirl-flow plasma arc lamps, ultraviolet lightemitting diodes, and ultraviolet light emitting lasers. Particularlypreferred ultraviolet light sources are "black lights" and medium orhigh pressure mercury vapor lamps, such as Models 60-2032, 60-0393,60-0197 and 50-2031 (commercially available from PPG Industries, Inc.),and Models 6512A431, 6542A431, 6565A431, and 6577A431 (commerciallyavailable from Hanovia, Inc.).

Ionizing radiation can also be used to cure the casting resins of thisinvention. Ionizing radiation is radiation possessing an energy at leastsufficient to produce ions either directly or indirectly and includesionizing particle radiation and ionizing electromagnetic radiation.Ionizing particle radiation designates the emission of electrons (i.e.,"E-beam" radiation) or accelerated nuclear particles such as protons,alpha particles, deuterons, beta particles, neutrons or their analogs.Charged particles can be accelerated using such devices as resonancechamber accelerators, DC potential gradient accelerators, betatrons,synchrotrons, cyclotrons, and the like. Uncharged particles (i.e.,neutrons) can be produced by bombarding a selected light metal such asberyllium with positive particles of high energy. Ionizing particleradiation can also be obtained by the use of an atomic pile, radioactiveisotopes or other natural or synthetic radioactive materials. Ionizingelectromagnetic radiation transmits high energy photons by means such asX-rays, bremsstrahlung and gamma rays.

Abrasion resistance is measured by determining the weight required toprovide a scratch in the surface of an article having a surface radiusof about 5 cm that is mounted below a weighted lever arm, the end ofwhich bears a 2 cm×2 cm patch of 000 steel wool that rests on thesurface of the article. The article is oscillated at about 30 pulses perminute through about 3 cm of an arc having a radius of about 5 cm.Weight is increased on the lever arm until a scratch is observed on thesurface of the article. The weight per square centimeter of surfacecontacting steel wool is then calculated as the scratch resistance ofthe article.

The following examples are offered to aid in understanding the presentinvention and are not to be construed as limiting the scope thereof.

EXAMPLE 1

This example illustrates the preparation of an urethane hexaacrylicester. Into a reaction flask equipped with an agitator, liquid additionfunnel, thermometer, and inlet tube for the introduction of dry air formaintaining an anhydrous atmosphere was placed 105 gisophoronediisocyanate and several drops of dibutyltin dilaurate(DBTDL). The resulting mixture was agitated and 448 g of pentaerythritoltriacrylate (the acrylic anhydride-pentaerythritol reaction producthaving a hydroxyl equivalent weight of 448) was added over a 30 minuteperiod. The mixture was agitated and heated until I.R. analysisindicated disappearance of the --NCO absorption peak (about threehours).

The urethane polyacrylate ester, as prepared, was placed into a mixingflask and 0.10% by weight of methyl benzoyl formate added. The contentsof the flask were stirred until completely mixed and filtered into astorage vessel which was evacuated at a pressure of about 10 Torr forabout five minutes to remove bubbles from the casting resin.

An ophthalmic lens mold was prepared by sandwiching a resilient annulargasket made of plasticized polyvinyl chloride between a 65 mm diameterglass die and a cover glass. The glass die had a polished, concave, highbase curve surface with a diopter of 6. The cover glass had a polished,convex surface with a diopter of 6. It was not necessary to clamp theassembly together.

The mold cavity was filled with casting resin by applying a pressure ofabout 0.5 Kg/cm² to the storage vessel containing the degassed castingresin, and conducting the casting resin from the storage vessel througha flexible tube to the mold cavity. A hollow needle attached to the endof the flexible tube was used to introduce the optical casting resininto the mold cavity through an opening made by puncturing the sidewallof the resilient annular gasket. After filling the mold, the needle waswithdrawn and the hole in the sidewall of the gasket was plugged with ascrew. The filled mold was placed under a 25 watt black light andirradiated for 2 to 10 minutes through both halves of the lens mold.After such exposure to ultraviolet radiation, the casting resin hadcured to about 70 to 80 percent of final hardness, and the temperatureof the cast article inside the mold had increased to about 74° C. Thecast article was removed from the mold and post cured by exposure toultraviolet radiation for an additional ten seconds on the convex side.The resulting ophthalmic lens was completely colorless, had a refractiveindex of about 1.51, a light transmission of greater than 90% and acenter thickness of about 1.0 cm. It had a Barcol hardness of 50 and anabrasion resistance of about 700 kPa (100 psi) on the convex side.

EXAMPLE 2

An urethane nonaacrylic ester was prepared by the procedure described inExample 1 from 90.5 g of the trimer of hexamethylene diisocyanate(available as KL5-2444 from Mobay Chemical Co.), 209 g pentaerythritoltriacrylate (having a hydroxyl equivalent weight of 411), and 6 drops ofDBTDL. The mixture was heated at 70° C. until the --NCO absorption peakdisappeared (about three hours).

An ophthalmic lens was prepared as described in Example 1. It had aBarcol, hardness of 50 and scratch resistance of about 620 kPa (90 psi)when post cured in air but a scratch resistance of greater than 830 kPa(120 psi) when post cured under nitrogen. It also had a refractive indexof 1.52 and a Gardner color of about 3 and a light transmission ofgreater than 90%.

EXAMPLES 3-8

This example illustrates the preparation of a polymerizable carbamiccompound (Formula II). Into a reaction flask equipped with an agitator,liquid addition funnel, thermometer, and inlet tube for the introductionof nitrogen atmosphere was placed 600 g (0.6 mole) of "Lexorez"5171-280, 1.5 g dibutyltin dilaurate, and 21. g "Irganox" 1010antioxidant[(tetrakis)3-[3,5-di(t-butyl)-4-hydroxyphenyl]propionyloxymethylmethane], commercially available from Ciba Geigy, Inc. The resultingmixture was agitated, and 465 g (3.0 moles) of 2-isocyanatoethylmethacrylate was added to the reaction flask over a 30 minute period,with the rate of addition of the 2-isocyanatoethyl methacrylate beingadjusted to keep the temperature of the reaction mixture from exceedingabout 75° C. A heating mantle was placed about the reaction flask, andthe reaction mixture was heated for an additional 30 minutes at atemperature of about 70° C. to 75° C., until infrared analysis of thereaction mixture indicated that the isocyanate groups had been consumed.The reaction product was allowed to cool, and designated "Oligomer A".

Oligomer A was blended with various amounts of pentaerythritoltetraacrylate and tetraethyleneglycol diacrylate and 0.1% by weight ofthe total composition of Vicure 55. A lens was prepared from eachcomposition by the procedure described in Example 1. The abrasionresistance of lenses prepared from each composition is given in Table I.

                  TABLE I                                                         ______________________________________                                        Lens           Experiment No.                                                 Casting Composition.sup.(a)                                                                  3     4      5   6    7     8                                  ______________________________________                                        PETA.sub.4.sup.(b)                                                                           10    20     30  40   45    50                                 Oligomer A     50    50     50  50   45    50                                 TEGA.sub.2.sup.(c)                                                                           40    30     20  10   10     0                                 Abrasion Resistance.sup.(d)                                                                  10     5     10  20   350-700                                                                             200-300                            ______________________________________                                         .sup.(a) Percent by weight of each component                                  .sup.(b) Pentaerythritol tetraacrylate                                        .sup.(c) Tetraethyleneglycol diacrylate                                       .sup.(d) Abrasion resistance in kpa                                      

It is apparent from Table I that Oligomer A diluted with up through 40%by weight of pentaerythritol tetraacrylate yields lenses that have anabrasion resistance of no more than 20 kPa, and that between 40 and 45%there is a surprising increase in abrasion resistance to above 350 kPa.By comparison, an uncoated lens prepared from diethyleneglycol bis(allylcarbonate), had an abrasion resistance of 20 kPa.

EXAMPLE 9

A polymerizable carbamic ester (Formula II) was prepared by melting in around-bottom flask 177 g 1,6-hexanediol and adding 449 g2-isocyanatoethyl methacrylate while cooling the mixture with a waterbath to maintain the temperature at 60° C. during the addition. Afterthe addition, heat was applied for one to two hours, after which timeinfrared analysis indicated disappearance of --NCO. The productsolidified on cooling the reaction mixture (m.p. about 55° C.).

The above carbamic ester was dissolved in an equal weight of warmpentaerythritol tetraacrylate and 0.1% by weight of Vicure 55 added. Alens prepared as described in Example 1 had an abrasion resistance of840 kPa and a Gardner color of 3. It also had a light transmission ofgreater than 90% and a refractive index of 1.52.

EXAMPLE 10

A casting composition was prepared by blending 50 g pentaerythritoltetraacrylate, 50 g 1,3,5-tris(2-acryloyloxyethyl)isocyanurate (FormulaIII), and 0.1 g Vicure 55. A lens was prepared from the composition asdescribed in Example 1. It had an abrasion resistance of 1050 kPa and aGardner color of 11 on the "b" scale.

EXAMPLE 11

A casting composition was prepared by blending 50 g of the reactionproduct of one mole of1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione,two moles of pentaerythritol triacrylate and one mole of 2-hydroxyethylmethacrylate (Part I) with 25 g of pentacrythritol tetraacrylate and 25g of 1,3,5-tris(2-acryloyloxyethyl)isocyanurate (Part II). There wasthen added 0.1% of Vicure 55 and a lens prepared as described inExample 1. The lens obtained had a refractive index of 1.52, wasessentially colorless and had an abrasion resistance of at least 500kPa.

I claim:
 1. An article having an inherent abrasion resistance to 000steel wool of at least 140 kPa comprising a polymerization product of(a)from 45 to 60 percent by weight of a polyacrylic ester; and (b) from 20to 55 percent by weight of a polymerization shrinkage modifiercomprising a polymerizable carbamic compound having at least two groupsselected from ##STR10## and at least two acrylic groups per 168 to 2000of molecular weight and a molecular weight of 168 to 5000 which is anacryloyloxyalkyisocyanurate of the formula ##STR11## in which: R⁷ ispolyvalent aliphatic group selected from R⁶ and ##STR12## in which R⁶ isan alkylene group having 1 to 6 carbon atoms or a 5- or 6-memberedcycloalkylene group having 5 to 10 carbon atoms and R¹¹ has a valence ofg+1 and is a polyvalent aliphatic group having 4 to 10 carbon atoms and,optionally, one caternary oxygen atom; g is an integer of 1 to 3; and(c) from 0 to 30 percent by weight of a diluent monomer; and (d) asource of free radicals.
 2. An optical article according to claim 1having an index of refraction of from 1.45 to 1.75, and a thickness ofat least 2 millimeters,
 3. An article according to claim 1 wherein saidpolyacrylic ester is derived from an alkane, a cycloalkane, or anazacycloalkene polyol, the polyol having up to 24 carbon atoms and theester having from 4 to 10 acrylocy groups and nitrogen, when present,being covalently bonded to the carbon of a carbonyl group.
 4. An articleaccording to claim 1 wherein said carbamic compound is1,3,5-tris(2-acryloyloxyethyl)isocyanurate.
 5. An ophthalmic lens inaccordance with claim
 1. 6. An opthalmic lens according to claim 5having an index of refraction of from 1.45 to 1.75.
 7. A colorlessoptical article according to claim 1, having a maximum thickness of atleast 2 millimeters.
 8. An optical article according to claim 3 whereinsaid polyacrylic ester is selected from the group consisting ofpentaerythritol tetraacrylate, dipentaerythritol hexaacrylate,pentaacryloyloxymethylethane,3,3,7,7-tetra(acryloyloxymethyl)-5-oxanonane, arabitol pentaacrylate,sorbitol hexaacrylate and the corresponding methacrylates, and1,3-bit(2-acryloyloxyethyl-5,5-dimethyl)-2,4-imidazolidinedione.
 9. Anarticle according to claim 1 wherein said acryloyloxyalkylisocyanurateis selected from the group consisting of1,3,5-tri(6-[2,2,2-(triacryloyloxymethyl)ethoxycarbonylamino]hexyl)-s-triazine-(1H,3H,5H)trione,1,3,5-tris(4-[2-(methacryloxy)ethoxy-carbonylamino]cyclohexyl)-s-triazine-2,4,6(1H,3H,5H)trioneand1,3,5-tris(3-[2,2,2-(triacryloyloxymethyl)ethoxy]-2-hydroxypropyl)-s-triazine2,4,6(1H,3H,5H)trione.10. An optical article according to claim 1 having a thickness of atleast 2 millimeters.
 11. An ophthalmic lens according to claim 2 or 10.12. An article according to claim 1 comprising the polymerizationproduct of from 45 to 50 percent by weight of said polyacrylic ester andfrom 40 to 55 percent by weight of said polymerization shrinkagemodifier.
 13. An article according to claim 1 or 2 having an inherentabrasion resistance to 000 steel wool of at least 700 kPa.
 14. Anoptical article according to claim
 13. 15. An ophthalmic lens accordingto claim
 13. 16. A self-supporting article according to claim 1.